1. Field of the Invention
The present invention relates to an inertial instrument, and more specifically pertains to vibrating gyroscopes.
2. Description of the Prior Art
Gyroscopes are well known for use as sensors for sensing angular velocity acceleration which information is necessary for determining the location, direction, position, and velocity of moving vehicles, for example. Vibrating gyroscopes, while providing advantages in size and cost, have exhibited quadrature torque generated in the gyroscope output axis, apparently because the dither drive for such vibrating gyroscopes couples energy into the output axis as a result of the non-orthogonality between the dither axis and the output axis. This angular acceleration torque on the output axis is according to current techniques accommodated by a closed-loop torque-to-balance servo loop by applying torque directly on the proof mass to cancel this torque. This torque has a 90 degree phase relationship relative to the signal created by rate inputs and is therefore called “quadrature torque”. As a result, the rate signal can be extracted by phase discrimination techniques. However, if the quadrature torque is large, as sometimes occurs, a small error in the phase of the feedback torque, at the dither frequency, will generate a substantial error in the rate measurement.
To overcome this problem of phase error, prior art techniques have been recommending the use of dc voltages on the electrodes of the proof mass, which in turn generate an alternating torque on the proof mass during each cycle of dither motion. Although this technique works well, the present invention takes an alternate simpler, and perhaps, a more elegant approach, to solving the problem.